1. Field of the Invention
The present invention relates, generally, to disk drive systems, data storage disks and processes of making and using the same with improved vibration inhibiting capabilities and, in preferred embodiments, to such systems, disks and processes which employ a stiffening structure, such as a framework of ribs, disposed within the disk.
2. Back Ground
Modern computers employ various forms of storage systems for storing programs and data. For example, various forms of disk drive systems have been designed to operate under the control of a computer to record information and/or retrieve recorded information on one or more recording disks. Such disk drives include hard disk drives which employ recording disks that have magnetizable (hard) recording material, optical disk drives which employ recording disks that have optically readable recording material, mageneto-optical (MO) disk drives which employ recording disks that have optically readable magenetizable recording material, or the like.
Conventional disk drive systems typically include one or more recording disks supported for relatively high speed rotation on a rotary spindle. For example, FIG. 1a shows a side view of portions of a conventional disk drive system, including a conventional data storage or recording disk 10 supported on a spindle 11. A disk drive motor (not shown) is operatively coupled to the spindle 11 for rotation of the spindle and the disk supported thereon. A recording and/or reading head 12 is supported by suitable head support structure (not shown) adjacent the recording surface of the disk. To simplify the disclosure, FIG. 1 is shown with a single recording disk 10 having a single recording surface and a single head 12. However, other conventional disk drive systems employ multiple disks, double-sided disks (disks with recording surfaces on both surfaces) and multiple heads.
For purposes of illustration, the disk 10 is described herein as an MO disk. As shown in FIG. 1a, the disk 10 has a central hub opening through which the spindle 11 extends, and is formed with multiple layers, including at least one substrate or support layer 14, a recording layer 15 supported on the substrate layer 14 and at least one protective layer 16 on the recording layer. Further layers, such as one or more layers of dielectric material, may also be included in the layered disk structure, for example, between the protective layer and the recording layer.
The disk 10 and spindle 11 are shown in a top view in FIG. 1b. The spindle 11 extends through a central opening, which defines an inside diameter, of the disk. The disk is secured at its inner diameter (ID), in a fixed relation with the spindle 11, and is supported such that the outer diameter (OD) portion of the disk is free from contact with other components. In this regard, the disk is clamped at its ID to the spindle 11 and is free at its OD. When the spindle 11 is rotatably driven, the disk 10 is cause to rotate with the spindle.
The head 12 is supported for movement in the radial direction of the disk, such that the head may be selectively positioned adjacent any recording location on the recording surface of the disk, as the disk is rotated. In operation, the head 12 is moved in the radial direction to align or register with a desired track location on the recording surface of the disk. Once aligned or registered with the desired track location, the head is operated to read or write information onto the recording surface at the desired track location. It is important to properly register the head with the track location to effect accurate reading or writing operations on the registered track.
Modern advances in disk drive technology have resulted in increased disk storage density and decreased track widths, such that greater amounts of information may be stored per given recording surface area. However, as track widths decrease (and storage density increases), the need for accurate head registration increases. In general, smaller track widths require greater head-to-track registration accuracies and have smaller alignment error tolerances. For example, for a disk with 10,000 tracks per inch, the track width is only about 100 .mu.in and the total allowable (tolerable) off-track mis-registration may be no more than about 10 .mu.in peak-to-peak.
Track mis-registration (TMR) may result from a variety of sources, including, for example, ball bearing non-repeatable run out, spindle-disk rocking vibrations and disk flutter. However, with recent and up-coming advances in disk drive spindle motor technology (including the introduction of hydrodynamic bearing spindle motors), the asynchronous vibrations caused by ball bearing non-repeatable run out and spindle-disk rocking vibration can be dramatically reduced. As a result, disk flutter can be a substantial factor in the cause of TMR.
Disk flutter can be generally characterized as the vibrations encountered by a disk, for example, as a result of fixing and supporting the disk only at its inside diameter to a rotary spindle. During rotation of the disk, the disk tends to vibrate in several modes.
For a given disk inner diameter (ID) to outer diameter (OD) ratio (ID/OD), the natural frequency of a disk is proportional to: ##EQU1## where h is disk thickness, R is disk outer radius, E is Young's modulus, .rho. is density and .nu. is Poisson ratio. The vibration amplitude per unit force is proportional to: ##EQU2## where .eta. is disk material loss coefficient and D is disk rigidity and is defined by: ##EQU3##
Disk vibrations may occur in several modes, depending on the input excitation frequency. Various vibration mode shapes for a disk having its ID clamped and OD free are represented by the top and side view diagrams of FIGS. 2a, 2b, 2c and 2d. The upper part of each of those figures shows a top view of a disk, with a shaded region indicating the nodal line(s) between vibration nodes. The bottom part of each of FIGS. 2a-2d shows a side-view representation of the vibration wave-shape of the corresponding vibration mode. A (m,n) mode represents the m and n nodal lines in the circumferential and radial directions, respectively. Thus, FIG. 2a represents a (0,0) mode vibration. FIG. 2b represents a (1,0) mode vibration. FIG. 2c represents a (0,1) mode vibration and FIG. 2d represents a (0,2) mode vibration.
Disk flutter may include one or more of the various vibration modes shown in FIGS. 2a-2b. MO media are particularly susceptible to the high amplitude of the (0,1), (0,2) and (1,1) vibration modes. These modes can greatly affect servo performance, since most servo systems have a limited bandwidth and rely on low amplitudes of the disk bending modes. Current MO media designs typically require a substantial increase in the disk thickness to reduce the amplitude of the above mentioned modes.